Helicopter rotor cyclic pitch control



Feb. 24, 1953 R. P. ALEX 2,629,452

HELICOPTER ROTOR CYCLIC PITCH CONTROL Filed May 20. 1947 5 Sheets-Sheetl RALPH PAUL ALEX Fig. 3 INVENTOR BYMZM ATTORNEY Feb. 24 1953 R. P. ALEX2.629,452

HELICOPTER ROTOR CYCLIC PITCH CONTROL Filed lay 20. 194? i'sheetssheet 2TAIL ROTOR DRIVE SHAFT ATTORNEY Feb. 24, 1953 R. PwALEX -;2,629,4s2.

HELICOPTER xoroascvcuc PITCH CONTROL Filed May 20, 1947 s shee s-sheet;Y

v AUTOROTATIVE POSITION BLADE PITCH CONTROL HORN g; FLAPPING HINGE 58POWER oN/ DAMPER I POSITION BLAD E STOP TOTAL PITCH CONTROL FORWARDRALPH PAUL ALEX INVENTOR ATTORNEY Feb. 24, 1953 R. P. ALEX HELICOPTERROTOR CYCLIC PITCH CONTROL Filed May 20, 1947 5-Sheets-Shet 4 g DRAGHINGE Q FLAPPING HINGE PITCH CONTROL ROD ROTATING BLADE REST STAR TORQUESCISSORS LATERAL CONTROL ROTOR PYLON I INCREASE PITCH T DECREASE PITCHTOTAL PITCH CONTROL FORWARD RALPH PAUL ALEX INVENTOR M Awa ATTORNEY Feb.24, 1953 R. P. ALE'IX 2,629,452

HELICOPTER ROTOR CYCLIC PITCH CONTROL Filed May 20. 1947 5 Sheets,-:Sheet5 i BLADE ROTATION I32 LATERAL CONTROL TOTAL PITCH CONTROL AFT PORTLONGlTUDlNAL I62 CONTROL STARBOARD FORWARD INCREASE we TOTAL PITCH ANDTHROTTLE CONTROL kg N, 54/STICK w W [I fl DECREASE \r AZIMUTH I44GOMPENSATING :F'i 3 I36 RALPH PAUL ALEX g INVENTOR BY ,afl/a Ma ATTORNEYPatented Feb. 24, 1953 HELICOPTER ROTOR CYCLIC PITCH CONTROL Ralph P.Alex, Stratford, Conn., assign'or to United Aircraft Corporation, EastHartford, 001111., a corporation of Delaware Application May 20, 1947,Serial No. 749,256

1 Claim. (01. 170 1s0.2'5)

This invention relates to helicopters and more particularly tosimplification of the rotor hub construction and the pitch changingmechanism so that the cost of production thereof may be materiallyreduced.

Accordingly, it is an object of this invention to provide a simpleclockcase type of rotor head construction wherein the component partsare mounted between a pair of similar plates.

Another object is to provide a helicopter Wherein the rotor blades willalways be normal to the flapping or coning axis.

A further object is to provide a blade rest which underlies the blade inall flight conditions.

Anether object is to provide blade stops which may be readily serviced.

A further object is to provide a system of freefloating control starswhich eliminates contact between the stars and the rotor drive shaft,thus eliminating bearing surfaces therebetween.

A still further object is to provide a swash plate system forcontrolling the blade pitch which is greatly simplified and cheaper toproduce.

Another object is to provide a simple but strong pitch control mechanismincluding the controls therefor.

Other objects and advantages will be apparent from the specification andclaim, and from the accompanying drawings which illustrate the presentlypreferred embodiment of my invention.

In the drawings,

Fig. 1 is a top plan view of a helicopter constructed according to myinvention;

Fig. 2 is a side-elevation2tl View of the helicopt'er shown in Fig. 1;

Fig. 3 is a front elevational view of the he'licop ter shown in Fig. 1;

Fig. 4 is an inboard profile or a side-elevation'al View with partsbroken away to show the general layout of the component parts;

Fig. 5 is a top profile view showing the relationship of the controls tothe pilot seat and of the engine with respect to the center line of theship;

Fig. 6 is a top plan view of the main rotor with parts hroke'n away toshow the component parts in detail;

Fig. 7 is a side-elevational View of the rotor shown in Fig. 6 withparts broken away; and;

Fig. 8 is a perspective showing of the dual control system for the bladepitch.

Referring to Figs. 1 through 3, a helicopter is shown having a bodygenerally denoted by the numeral I0, which is comprised of a centralportion I 2 which houses the engine and has the main rotor l4mounted'thereon', a forward portion comprising a pilots compartment, anda tail cone 16 which has a tail rotor l 8 and the tail rotor pylon 20mounted thereon. The landing gear "for the helicopter consists of asmall nose wheel 22 and two laterally disposed wheels 24. A tail skid2'! is mounted on the tail rotor pylon 20 to protect the tail rotorblades from damage in case of a tail down landing.

Referring now to Figs. 4 and 5, the engine 28 is mounted in the centralportion I2 of the helicopter body with its drive shaft in a verticalposition and is surrounded by a cowling 3B which is open at the top toadmit engine cooling air. An engine driven fan 32 is mounted within andjust below the throat of the cowling 30' to blow the cooling airdownwardly and over the engine cylinders. The cooling air is drawnthrough an opening 33 (Figs. 2 and 3) in the upper portion of the fuse--lage just forward of the main rotor drive shaft 28 and is exhaustedthrough the grill 34 in the after portion of the central section of thefuselage. The engine drive shaft 36 drives the main rotor l4 and thetail rotor l8 through reduction gearing contained within housing 38. Onthe upper portion of the reduction gear housing 38 is the drive take-off40 for the tachometer generator (not shown). The tail rotor drive shaft42 is driven at a high speed from this take ofi and the speed thereof isreduced in reduction gearing in the tail rotor pylon 2B. This enablesthe long tail rotor drive shaft 42 to be of small diameter,

The pilots compartment is separated from the engine compartment by afirewall 46 and provides seating capacity for two persons. This sectionis comprised primarily of transparent plastic to 9.1- ford a wide rangeof visibility which is compatable with the extreme maneuverability ofthis type of aircraft. The transparent plastic sections on the topportion of the pilots compartment are prefer ably dyed green to reducethe glare of the sun.

The occupants of the pilots compartment sit side by side in seats 48. Aninstrument box 59 is provided between the seats 48 in a forward positionwithin the transparent plastic nose bubble.

Dual controls are provided and consist of an azimuth control stick 52,a, total pitch and throt tle control stick 54, and root pedals tocontrol the pitch and consequently the torque of the tail rotor is. Theazimuth stick 52 and the total pitch stick 54 control the pitchsetting'of the main ro-' tor blades as in a manner which wiii be morefully explained hereinafter.

Referring now to Figs. 6 and 7, which show the details of the hubassembly and the pitch controls, the blades 58 are of all metalconstruction and are fabricated accordin to the method disclosed in thecopending U. S. app ication Ser. No. 632,620 of Igor I. Sikorsky,assigned to the applicants assignee, and issued August 12, 1952, asPatent No. 2,606,728.

The main rotor drive shaft 28 drives the hub through splines 60. The hubis comprised of two similar plates 62, 52 which are generally triangularin plan and are separated from each other to permit mounting theessential parts therebetween. In this construction it will be noted thatthe hub is fabricated in a manner similar to that employed in clockcases where all the parts are mounted between the two faces. Thevertical drag hinge 64 is mounted between the two hub plates 62, 62 onsubstantially the extended radius of the drive shaft 25. The horizontalor flapping hinge 66 intersects the drag hinge 64 at 90. The stub shaft08 is pivotally mounted on the flapping hinge 80. A sleeve member I ismounted on the stub shaft 68 by means of bearings I2 which allow thesleeve I freedom of rotation but prevent axial movement. The blade 58 ismounted on a spar I4 which is held fixed with respect to the sleeve I0by means of a threaded retention member I6.

As shown in Fig. 6, the blades are in the autorotative position, i. e.,the longitudinal axis of each blade is substantially aligned with aradius of the drive shaft 26. In the power-on position, the blades willdrag back to the position shown in dotted lines. These two positionsrepresent substantially the magnitude of the blade movement around thedrag hinge which is desirable. Movement beyond these positions must berestrained and for this purpose blade stops I8 have been mountedvertically between the hub plates 82 by means of bolts 80. The bladestops I8 have rubber cushions 82 mounted on the contacting faces to easethe shock of contact. A paddle shaped finger 84 extends inwardly fromthe drag hinge pin 64 and is integral therewith. The paddle 84cooperates with the rubber cushions 82 on the blade stops 18.

Movement of the blade 58 in a vertical plane about the flapping hinge isdesirable in flight but the blade must be restrained from movement belowa horizontal position so that the blade tips will not strike the groundor the tail cone I5. To restrain such movement, a blade rest 86 has beenprovided by merely extending a finger outwardly from the drag hinge asbest shown in Fig. 7. A rubber cushion 88 is bolted on the stub shaft 88to cooperate with the blade rest.

Movement of the blade about the flapping hinge 66 results fromaerodynamic and dynamic forces and need not be restrained but movementabout the drag hinge 64, resulting from the natural hunting action ofthe blade in forward flight, must be clamped to avoid excessivevibration. Accordingly, a damper 90 is provided for each of the blades58 and is mounted vertically between the hub plates 62. The movement ofthe blade about the drag hinge is transmitted to the damper arm 92 bymeans of a link 94 and an arm 96 which is secured on a serrated verticalextension of the vertical hinge 64 by means of a lock nut 98.

The blade pitch control horn I00 is integral with the rotatable sleeveI0 and the blade stub spar I4. Movement of the control horn I00 willchange the pitch of the blade 58. As best seen in Figs. 6 and '7, thecontrol horn I00 is connected to the pitch control rod I02 at a pointlying on the extended axis of the flapping hinge. Since the flappinghinge moves with the blade 58 about the drag hinge, this point ofconnection will always lie on the extended axis of the horizontal hinge66. Therefore as the blade moves about the flapping hinge, there will beno delta-3 effect, i. e., no decrease in pitch as the blade movesupwardly about the flapping hinge. If it is desired to have a delta-3effect, the point of connection between the control horn I00 and thecontrol rod I02 may be moved off the center line of the flapping hingeand away from the axis of the drive shaft 26.

The lower end of the pitch control rod I02 is pivotally connected at I04to the rotating star I06 which is driven at rotor speed by means oftorque scissors I01. The star I06 is rotatably mounted on the stationarystar I08 by means of bearings I I0 which allow relative rotation betweenthe stars but maintain them parallel. The stationary star I08 may bemoved axially with respect to the drive shaft 26 or tilted in anydirection by movement of the total pitch stick 54 and the azimuth stick52 in a manner to be more fully described hereinafter. A lever H2 ispivoted at H4 on an upwardly projecting arm II6 which is integral withthe rotor pylon I I8. The pylon I I8 provides bearings I I9 for theshaft 26. Since the rotor pylon H8 is part of the fuselage framework,the pivot point II4 provides a rigid stationary reference point. Theleft hand end of the lever H2 is pivotally connected at I28 to rod I3.The right hand end of the lever I I2 is pivotally connected by means ofbearings I20 to an inner ring I22 which is pivotally connected by meansof pins I24 to an outer ring I26. The lateral control arm I32 isconnected to the outer ring I26 and extends generally aft and to theleft with respect to the fuselage. A longitudinal control arm I34 (Fig.'8), extending aft and to the right is connected to the outer ring I26at substantially to the lateral control arm I32.

It will be noted that the pitch control rod I02 is substantiallyvertical in the auto-rotative position shown in the drawings. When theblades drag back, in power-on flight, the control rod I02 will becomeslightly inclined. As the hunting action takes place, the blade will bedamped aerodynamically as well as by the dampers 90. Thus as the bladedrags back the control rod I02 becomes further inclined and the pitch ofthe blade 58 is decreased to allow the blade to swing forwardly.Conversely, as the blade swings forward, the control rod I02 approachesthe vertical position and increases the pitch of the blade to cause itto move back to the normal power on position.

Movement of the rod I30 will act to increase or decrease the pitch ofthe blades simultaneous- 1y. As the rod is moved down, the lever II2rotates about the pivot II 4 in a counterclockwise direction to moveboth stars upwardly and increase the pitch of the blades. Similarly,when the rod I30 is moved up the pitch of the blades will be decreased.

Cyclic variations in the pitch are obtained by moving the lateral orlongitudinal control arms singularly or conjointly, dependent upon thedirection of flight which is desired. It should be noted here that theinbuilt 90 lead of the control horn, customary in prior productionhelicopters, is not utilized in this rotor construction. In the priorconstruction the stars were inclined in the direction of flight and the90 control horn lead allowed for the aerodynamic control lag." However,in the instant construction the stars are inclined approximately 45ahead of the tip path plane. For example, the stars are inclined forwardand to the left to obtain forward flight and inclined. aft and to theleft to obtain flight to the left.

The simplified control mechanism for obtaining the desired movement ofthe stars I06, I08 is showninl igs. 7 and 8. Directional control offlight is obtained. by moving either or both of the azimuth controlsticks 52. These control sticks are interconnected by rods I33, I sothat the movement of one stick will cause corresponding movement of theother. The pivot connections for each of these sticks is the same asthose employed for the other; therefore, the description of operationwill belimited to consideration of but one stick.

When the pilot desires to move forward, the control stick 52 is movedforward to rotate the bell crank I36 about pivot I38 and move the rod Iaft. Movement of rod I will rotate the lever I42 about pivot I44 toraise rod I 46, rotate the torque rod I48 which is mounted in fixedbearings I 41, I49 and raise rod I50, and the longitudinal arm I34 totilt the stars I06, I08 forward and to the left or port side. As pointedout hereinbefore when the stars are so tilted the motion of thehelicopter will be forward since the control horn does not lead thecontrol application by 90'. will move rods I46 and I50 down to tilt thestars aft and to the right, giving a backward tilt to the tip path planeof the rotor blades and backward flight.

When it is desired to move to the right, the control stick 52 is movedto the right which causes rotation of the torque rod I52 which ispivotally mounted in a bodily fixed bearing I 54 and in floatingbearings I56, I51. When the torque rod I52 is rotated in this manner thelaterally disposed arm I58 will push up on rod I60 to rotate torque rodI62, mounted in fixed bearings I 6i, I53, and raise lateral control rodI64. This will tilt the stars forward and to the right, inclining thetip path plane to the right to give flight to the right. Similarly, whenthe azimuth control stick 52 is moved to the left, arm I58, rod I60, androd I64 will be moved down to tilt the stars aft and to the left toincline the tip path plane to the left.

Of course, motion of the azimuth control stick 52 need not be limited tothese four directions but may be in any direction to cause flight of thehelicopter to be in such a direction. It will now be apparent that thenecessary 90 lead has been incorporated in the control mechanism for thestars rather than in the control horn.

Movement of the total pitch and throttle control stick 54 will act toincrease or decrease the pitch setting of all the blades simultaneously.

When the pitch is increased the throttle setting will be correspondinglyincreased to maintain the required engine R. P. M. through well-knownsynchronizing mechanisms. Adjustments of the throttle setting may be hadby movement of the handle portion of the stick 54 after releasing anautolock mechanism. The details of this synchronization and adjustmentform no part of this invention.

When the pilot pulls the total pitch stick 54 upwardly, the stickrotates about fixed pivots I66 to move arm I53 and rod I III down. Whenthe rod I10 is moved down, the torque rod I12 mounted in fixed pivotsI'II, I73 is rotated to move the total pitch rod I30 down and rotateSimilarly, movement of the stick 52 aft 1 the lever H2 about pivot H4 toraise the stats. It will be apparent that, due to the universalconnection of lever Hi! to the lower star I08. the stars would be tiltedif the lateral and longitudinal control arms are held fixed. Itistherefore necessary to compensate for movement of the total pitch stickso that the lateral and longitudinal arms will be moved a correspondingamount. Accordingly, an azimuth compensating link lid is mounted forrotation about the pivot I56 conjointly with movement of the total pitchstick 54. Thus, as the stick 54 is pulled up to increase the pitch, theazimuth compensating link IN is moved upwardly and lifts torque rod I 52a predetermined amount. Raising the torque rod I52 raises the points ofconnection to the rods Hi5 and Iliii and causes upward movement of thelateral and longitudinal control arms to compensate for movement oflever I I2.

By utilizing this free-floating construction of the rotating andstationary stars mounted on the rotor pylon, it has been possible toeliminate bearing contact between the stars and the drive shaft 25. Thecombination of the free-floating stars and the clockcase hub results ina great simplification and saving in production costs.

Referring back to Fig. l, as the blades 58 rotate in the clockwisedirection indicated, there will be a reaction couple R-R exerted aboutthe vertical axis of the helicopter. The tail rotor I8 exerts a thrust Tin the direction indicated to overcome the torque of the main rotor.However, since a couple is necessary to counteract another couple, it isnecessary to exert another force in the same plane as the reactioncouple R-R and the torque force T. As the tip path plane of thehelicopter is inclined to the right, a force I is obtained. Now thereaction couple RR is counteracted by the couple 'I-I. Heretofore theinclination of the tip path plane has been achieved by inclining thecontrol mechanism. In this helicopter, however, the control mechanism isnot inclined with respect to the rotor shaft and the necessary lateralforce I is obtained by offsetting the center of gravity of thehelicopter with respect to the longitudinal axis thereof.

Referring now to Fig. 5, it will be apparent that the drive shaft andconsequently the center of gravity of the engine 28 is offset from thecenter line of the helicopter. The reduction gearing 38 acts to reducethe engine speed to rotor speed and also to drive the rotor drive shaft26 on the longitudinal center line of the helicopter. Since the weightof the engine is offset from the center line, the center of gravity ofthe helicopter is also offset. This will cause the entire helicopter tobe slightly inclined to the right, resulting in a similar inclination ofthe tip path plane of the rotor blades. Under these conditions, thenecessary lateral force I is obtained without inclining the controlsystem relative to the rotor shaft. The inclination of the helicopter tothe right is only a matter of one or two degrees and, therefore, causesno passenger discomfort.

While I have shown and described one presently preferred modification ofthis invention, obviously other modifications and adaptations will occurto those skilled in the art; therefore, I wish not to be limited in myinvention only to the form shown and described, but by the scope of thefollowing claim.

Iclaim:

In rotary wing aircraft, a rotor drive shaft, a hub on said shaft, adrag pivot having its axis oifset from the axis of said shaft, aflapping pivot 7 having its axis intersecting the axis of said dragpivot, a stub shaft pivotally mounted on said flapping pivot having itslongitudinal axis perpendicular to the axis of the latter, a bladejournalled on said stub shaft for blade pitch changing movements aboutthe longitudinal axis of the latter, and means for controlling saidblade pitch including a swashplate, a pitch control horn on said bladehaving its extended end terminating substantially on the axis of saidflapping pivot,

and an external link extended from said swashplate to said horn andjournalled on the latter near the extended axis of said flapping hingein all positions of the blade around said drag pivot, the axis of saidflapping pivot being always at right angles to the blade feathering axisand said flapping pivot carrying with it the blade pitch control hornfor all lead-lag positions of the blade with respect to the drive shaft.

RALPH P. ALEX.

REFERENCES CITED The following references are of record in the file ofthis patent:

8 UNITED STATES PATENTS Number Number Name Date Larsen Feb. 20, 1934Cierva Mar. 6, 1934 Pecker Aug. 21, 1934 Breguet Jan. 1, 1935 Platt Mar.23, 1937 Campbell July 5, 1938 Pecker Mar. 7, 1939 Pullin Dec. 28, 1943Pitcairn June 27, 1944 McDOugal Mar. 12, 1946 Jenkins Apr. 2, 1946Cierva May 27, 1947 Campbell Sept. 30, 1947 Hirsh Nov. 11, 1947 HodsonApr. 6, 1948 Pullin Apr. 20, 1948 FOREIGN PATENTS Country Date FranceFeb. 3, 1936

